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The evolution of the bipedalism was accompanied by significant evolutions in the spine including the forward movement in position of the foramen magnum, where the spinal cord leaves the cranium.

Suggestions
I had a couple of suggestions for this article. First, while this is over the evolution of bipedalism in general, I think this article could talk more in depth about the specific lineages and evolutions leading up to bipedalism in humans as well as after. Also, the evolution of sexual dimorphism/lumbar spine that accompanied bipedalism could be made into its own paragraph in this article. It is only briefly mentioned. Lastly, the theories as to why amphibians and reptiles never developed bipedalism could be added to the respective sections within this page. Stephensen.2 (talk) 13:07, 1 October 2014 (UTC) Sam Stephensen

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Around 3.8 million years ago, the first bipedal hominins walked the Earth (Langdon 1985). Bipedalism has evolved multiple times throughout evolutionary history. One example is in birds, the evolutionary ancestor of dinosaurs, who also displayed bipedalism (Snyder 2006). Bipedalism is the defining feature in the divergence of apes and hominoids, and is unparalleled among all land-dwelling vertebrates, but little is known about why and how it evolved. The advent of bipedalism began a cascade of evolutionary changes in early hominins.

Paper
Around 3.8 million years ago, the first bipedal hominins walked the Earth (Langdon 1985). A major evolutionary change, bipedal locomotion allowed for a complete reorganization of the hominoid body plan such as changes in the size of joints, an orthograde posture and increased brain size (Snyder 2005). Bipedalism is the defining feature in the divergence of apes and hominoids, and is unparalleled among all land-dwelling vertebrates, but little is known about why and how it evolved. What are possible reasons for this major evolution to occur and what are the effects of such an evolution? Bipedalism has evolved multiple times throughout evolutionary history. One example is in birds, the evolutionary ancestor of dinosaurs, who also displayed bipedalism (Snyder 2006). While prevalent throughout biology, bipedalism in hominins is markedly different. The largest difference between bipedalism in hominins and any other species is posture. Hominins are the only species to habitually have a balanced, orthograde posture, which resulted directly from bipedalism (Prost, 1980). But, how did this separation between early hominins and apes occur? It is unknown whether we descended from “knuckle-walkers” or arboreal species; however, compared to “knuckle-walkers” it is assumed bipedalism evolved in early hominins as a result of decreased locomotive cost (Prost 1980). As hominins began to walk upright, they placed increasing amounts of pressure on joints (Sylvester, 2006). This ultimately led to changes in the morphology of hominins including the lengthening of femoral bones as well as a distinctive big toe. Other key adaptations in hominins include the axial rotation of the pelvis and a reduction in shoulder mobility (Sylvester, 2006). Bipedalism in hominins is unique, but why? What advantages or disadvantages does this type locomotion pose? Bipedalism is a type of locomotion in which the subject moves upright with only two legs; it allows the subject to stand, walk, run and jump. This type of locomotion has many disadvantages as well as advantages. One of the largest disadvantages is a high-energy cost. An imperfect upright stance causes high-energy consumption with locomotion in bipeds (Niemitz, 2010). Over evolutionary time, hominins developed multiple adaptations that improved stance and made bipedalism highly efficient. Just as well, control of forward momentum, along with balancing mechanisms, are compounded in bipeds causing them to be more unstable and slower than quadrupeds, ultimately adding another disadvantage to bipedalism (Price, 1993). Bipedalism advantages include an upright posture, which in turn means a greater range of sight as well as the freedom for specialization of forelimbs, which are no longer used in regular locomotion (Hunt, 1996). These advantages and disadvantages make it hard to determine how exactly bipedalism evolved. As mentioned, a greater range of view is an advantage of bipedalism. Could this have fueled its’ evolution? The “watching out” hypothesis suggests this advantage was a primary driver for the evolution of bipedalism (Hunt, 1996). Baboons and Chimpanzees have been observed standing up to watch out for predators. However, the rate of bipedal standing in this species is very small (Hunt, 1996). The “savannah” hypothesis is another possible answer as to why the evolution of bipedalism occurred in early hominins. This hypothesis postulates that around four to two million years ago grasslands in eastern Africa became increasingly widespread while wooded areas declined (Langdon, 1985). This reduction in trees led to early hominins walking in search of food and cover as well as a need for the arms to carry objects. It is assumed Hominins who adapted bipedalism experienced a higher fitness relative to non-bipeds as it allowed for these animals to search for food at lower costs (McHenry, 1986). A significant downfall to this hypothesis, however, is the unusual weight distribution in apes. A high center of mass and a relatively small support structure would have made biped hominins clumsy, however, selective pressures may have overcome this (Snyder, 2005). Another part of the savannah hypothesis takes display behaviors into account. This part of the savannah hypothesis argues that bipedal displays determined intragroup conflicts and as result became a highly selected trait. The savannah hypothesis is one of the longest-standing models for the evolution of bipedalism. Another hypothesis, the provisioning model, also gives a possible answer to this evolutionary question. This model explains bipedalism by the need of arms and hands for carrying objects instead of locomotion. Studies of chimpanzees show a bipedal gait allows for efficiency when carrying food or other objects, such as tools (Niemitz, 2010). The provisioning model allowed for the carrying of babies as well. Provisioning in early hominins was also the result of an ever-growing investment in parental care and monogamy. The carrying of food increased direct fitness by increasing the survival rate of infants and mates (Prost 1980). This again would lead to a high selection for bipedalism. A final hypothesis offered for the evolution of bipedalism is the wading model. The wading model hypothesizes that on shores high quality food could be obtained with little investment (Niemitz, 2010). Of all the hypotheses, this is the only behavior that demands an upright posture and bipedal locomotion. The wading model poses several advantages that may have selected for bipedalism. The first of which is the reduction of weight in submerged body parts (Niemitz, 2010). As mentioned earlier, poorly postured bipeds experience high-energy costs. This would have greatly reduced the weight carried by early hominins legs as well as back and also reduced energy costs. Wading would have also selected for long-legged individuals as they could go further from shore (Richmond, 2008). The wading model is a relatively new idea that could become increasingly likely with more evidence. The advent of bipedalism began a cascade of evolutionary changes in early hominins. As hominins began to walk upright, they placed increasing amounts of pressure on joints (Sylvester, 2006). This ultimately led to significant changes in the morphology of hominins. Other key adaptations include the axial rotation of the pelvis and a reduction in shoulder mobility (Sylvester, 2006). While it is not clear now, future research may bring to light the last the common ancestor we share with apes as well as the cause behind our divergence from them. Bipedalism represents a major shift in the separation of humans and apes, and is the causation of many features we see in ourselves today. References Mchenry, Henry M. The First Bipeds: A Comparison of the A. Afarensis and A. Africanus Postcranium and Implications for the Evolution of Bipedalism. Journal of Human Evolution 15.3 (1986): 177-91. Web. Richmond, Brian G., and William L. Jungers. Orrorin Tugenensis Femoral Morphology and the Evolution of Hominin Bipedalism. Science, 2008. Print. Niemitz, Carsten. The Evolution of the Upright Posture and Gait – a review and a new synthesis. Naturwissenshaften, 2010. Web. Price, T. Douglas, and Gary M. Feinman. Images of the past. Mountain View, CA: Mayfield Pub., 1993. Print. Sockol, Michel D., Raichlan, David A., and Pontzer, Herman. Chimpanzee locomotor energetics and the origin of human bipedalism. Cambridge, MA: Harvard University, 2007. Web. Sylvester, Adam D. Locomotor decoupling and the origin of hominin bipedalism. Jornal of Theoretical Biology. 2006. Web. Snyder, Richard C. Adaptive Values of Bipedalism. American Journal of Physical Anthropology Seattle, WA. University of Washington. 2005. Web. Prost, J.H. Origin of Bipedalism. American Journal of Physical Anthropology. Chicago, IL. University of Illinois. 1980. Web. Langdon, John H. Fossils and the Origin of Bipedalism. Journal of Human Evolution. Indianapolis, IN. India Central University. 1985. Web. Hunt, K. D. The postural feeding hypothesis: an ecological model for the evolution of bipedalism. South African Journal of Science. 92:77–90. Web.